Mitsubishi VRF (City Multi) LEV issues

[kaon]

Here is a well-written LEV guide by Thermatech dated 18 July 2009.

However, I have a question about this part:

If you want to fully remove the LEV valve head from the valve body always turn power to the indoor unit off. The indoor unit will motor the valve needle into shut possition using the 30v dc control voltage.
If you hold the valve head in your hand you can feel it working & know when it has stopped at shut.
At this point the circuit board & you both know that the position of the valve is at shut possition.
Then if you put that valve head on another indoor unit provided you made sure that LEV valve was also fully shut before you removed it then you can do the swap.

Is this because the valve head does not know its absolute position and cannot tell the circuit board its absolute position?

What if the valve head has been removed from the valve body while still electrically connected, and then the indoor unit is switched off? Will the valve head motor to a longer-than-normal-close position? Is this bad?

Does anyone like to share more knowledge about these LEVs used in Mitsubish VRF? In my experience, they are super prone to problems, and also rust easily.

Thermatech mentioned strainers, are they integrated with LEV body?

[Ian21081974]

Hi

I've had loads of problems with these on a certain site.
When you remove the head make sure you power down the fcu and disconnect mnet.
And use two spanners too loosen.
Then once in place with the new hand tight valve then just gently nip it up very gently as I found out twice.
Then reconnect mnet and power up.
Fingers crossed time.

Ian

[Thermatech]

Perhaps I could clarify this a bit more.

The indoor circuit board makes position 2000 pulse fully open & position 41 pulse closed. The distance the needle travels is less than 2mm.
How does the circuit board know the position of the needle relative to the valve seat ?
It calibrates itself by motoring the needle down hard into the valve seat & holds it there for a couple of seconds then backs the needle out from the valve seat to position 41.
The circuit board needs to do this because the exact position of the needle depends on how tightly the head has been screwed down onto the valve body.

You will notice that a new spare part LEV valve comes with the head attached to the valve body & the valve is in an open position which you can confirm by blowing through the valve body.
If you want to replace just the valve head its a good idea to screw down the new head onto the old valve body with the new head still in this open position because then there is no risk of over tightening & jamming the needle in the valve seat. Then plug into the circuit board & turn on 240v power.


If you plug into the circuit board 1st & power up before tightening down the head onto the valve body then the head motors to the closed position & then when you tighten up with 2 spanners you risk over tightening & jamming the needle hard down into the valve seat which permanently locks the whole mechanism in the closed position & the tiny little motor will not be able to move the needle which is why Ian suggested reconnect Mnet & power after tightening.

If you look into the copper tubes on the LEV valve body you will see there are no strainers in the valve body.

Next time you replace an LEV valve put it in a vice & cut it open with a small hacksaw. All becomes clear once you can see the internal mechanism of the motor head & the valve body.

You can at any time carry out an LEV valve reset procedure which will force the circuit board to re-calibrate
1/ switch off 240v
2/ disconnect Mnet from circuit board ( usually blue plug )
3/ switch 240v on & confirm head motors to shut. Provided you have good hearing you should be able to listen carefully or hold the valve head in your hand.
4/ switch 240v off
5/ reconnect Mnet to circuit board
6/ switch on 240v
7 test indoor unit in heating & cooling to confirm refrigerant flow by TH2 TH3 & Superheat / subcool data